1. Field of the Invention
This invention relates to magnetic memory devices, and more particularly, to field-inducing line configurations arranged adjacent to magnetic cell junctions.
2. Description of the Related Art
The following descriptions and examples are given as background information only.
Recently, advancements in the use of magnetoresistive materials have progressed the development of magnetic random access memory (MRAM) devices to function as viable non-volatile memory circuits. In general, MRAM circuits exploit the electromagnetic properties of magnetoresistive materials to set and maintain information stored within individual magnetic memory cell junctions of the circuit. In particular, MRAM circuits utilize magnetization direction to store information within a memory cell junction, and differential resistance measurements to read information from the memory cell junction. More specifically, information is stored within an MRAM cell junction as a bit, the state of which is indicated by the direction of magnetization within one magnetic layer of the memory cell relative to another magnetic layer of the memory cell. In addition, a differential resistance can be determined from magnetization direction differences between the magnetic layers of the memory cell such that the state of the bit stored in the MRAM cell junction may be read.
Typically, an MRAM device includes a plurality of conductive lines with which to generate magnetic fields. In some cases, the conductive lines may be referred to as “bit” and “digit” lines. In particular, “bit” lines may refer to conductive lines arranged in contact with magnetic cell junctions that are used for both write and read operations of the memory cell junctions. “Digit” lines, on the other hand, may refer to conductive lines spaced adjacent to the magnetic cell junctions that are used primarily during write operations of the magnetic cell junctions. In general, an MRAM device may include a plurality of parallel bit lines spaced perpendicular to a plurality of parallel digit lines such that overlap points exists between the sets of parallel lines. Magnetic cell junctions as described above may be interposed between the conductive lines at such overlap points, such that an array of magnetic cell junctions may exist. During a write operation of an individual magnetic cell junction, current may be applied to the bit and digit lines corresponding to the particular memory cell such that a magnetic field may be created with which to orient the magnetic direction of the magnetic cell junction. Such an individual memory cell may herein be referred to as a selected memory cell, or the memory cell intentionally targeted for a writing procedure.
During the writing procedure, however, a multitude of other magnetic cell junctions arranged along the bit line and the digit line corresponding to the selected cell will also sense current. Such magnetic cell junctions are herein referred to as half-selected cells, or disturbed cells, since the magnetic field induced about the cells is generated from a single line rather than both the bit and digit lines. Even though less current is applied to these disturbed cells, variations within the cell junctions may allow a bit to be unintentionally written to one or more of the disturbed cells. The variations present within an array may include variations in the shapes and sizes of magnetic cell junctions, as well as the presence of defects. Such variations of the cell junctions may cause the amount of current needed to switch magnetic cell junctions in the array to vary, thereby reducing the reliability of the device. In this manner, the write selectivity of the MRAM array may be reduced. Write selectivity, as used herein, may refer to the ratio of selected cells and disturbed cells switched during a write operation of the device.
In general, the magnetic vectors within a magnetic layer will naturally align with the peripheral outline of the layer. As such, in some cases, an MRAM cell junction may be configured to initiate the switching mechanism used to change the magnetic direction of the cell at a particular point within the MRAM cell junction. For example, some conventional MRAM cell junctions are patterned to include rounded edges along opposing sides of the MRAM cell junction and substantially straight edges along other edges of the MRAM cell junction. In general, the magnetic vectors within regions of the MRAM cell junction including the rounded edges may be angled or curved with reference to the magnetic vectors aligned with the substantially straight edges of the MRAM cell junction since the magnetic vectors naturally align with the periphery of the layer.
Consequently, the magnetic vectors within the rounded edge region of the magnetic cell junction may be apt to switch their magnetic direction before the magnetic vectors aligned with the substantially straight edges of the magnetic cell junction. In addition, the switching mechanism of the magnetic vectors within the rounded edge region may activate the magnetic vectors arranged aligned with the substantially straight edges to change direction. In this manner, the starting point of the switching mechanism may be aligned with rounded edges of the MRAM cell junction. Consequently, lower current may be applied to switch a magnetic direction of an MRAM cell junction with rounded edges than an MRAM cell junction having substantially straight edges along all sides of the cell junction. However, as the need for lower power consumption within MRAM devices increases, further applications for reducing current requirements to switch the magnetic directions of MRAM cell junctions are needed.
Accordingly, it may be advantageous to develop an MRAM device configuration that further reduces the current needed to switch magnetic directions of MRAM cell junctions. In addition, it may be advantageous to develop an MRAM device configuration that offers more accurate and uniform write selectivity within an MRAM array.